Gear blanks

ABSTRACT

A centrifugally cast bi-metal gear blank having an outer annular rim of tin bronze, an inner annulus of yellow brass and a diffusion zone between said outer annular rim and said inner annulus, whereby there is a metallurgical bond between the tin bronze of the outer rim and the yellow brass of the inner annulus in said diffusion zone.

United States Patent [1 1 Miller 1 Nov. 12, 1974 [54] GEAR BLANKS 3,589,875 6/1971 Oakes 29/199 [76] Inventor: William H. Miller, 877 Valleyview Rd., Pittsburgh, Pa. l5243 [22] Filed: Aug. 20, 1973 [21] Appl. No.: 389,873

[52] US. Cl 29/191', 29/199, 164/84 [51] Int. Cl 8221! 13/00 [58] Field of Search 29/191, 199

[56] References Cited v UNITED STATES PATENTS R27,659 6/1973 Wolfe et al. 148/127 Primary Examiner-Winston A. Douglas Assistant Examiner-O. F. Crutchfield [57] ABSTRACT A centrifugally cast bi-metal gear blank having an outer annular rim of tin bronze, an inner annulus of yellow brass and a diffusion zone between said outer annular rim and said inner annulus, whereby there is a metallurgical bond between the tin bronze of the outer rim and the yellow brass of the inner annulus in said diffusion zone.

9 Claims, 2 Drawing Figures PATENTED NOV 12 L974 Hal GEAR BLANKS This invention relates generally to gear blanks and to a method of manufacturing the same and more particularly to bi-metal centrifugally cast gear blanks.

Gear blanks are generally made from a single metal such as tin bronze, and the gear teeth are machined on the outer periphery of the blank in manufacturing a finished gear. These gear blanks are cast according to well-known casting procedures and are expensive due to the high cost of copper which is present in significant amounts in tin bronze. In an attempt to decrease the expense, composite gear blanks have been manufactured with the outer annular rim made of tin bronze and the inner annulus made of a less expensive ferrous base alloy such as gray iron or ductile iron. An example of this type of gear blank is disclosed in U.S. Pat. No. Re. 27,659.

A composite gear blank requires some means for attaching the outer annular rim to the inner annulus. In the past, attachment has been effected by welding, by mechanical fasteners such as screws and rivets, by shrinking the inner periphery of the outer rim over the outer periphery of the inner annulus and pinning the two parts together, and by casting the outer rim around the inner annulus and forming a mechanical interlock between the two. Additionally, the outer rim has been attached to the inner annulus by soldering in the manner disclosed in the aforementioned patent. While a composite gear blank is less expensive than a gear blank made completely of tinbronze, the manufacturing cost is not as low as desirable due to the assembly and attachment of the parts. Furthermore, a lack of strength at the joint between the rim and the inner annulus can create failure problems when the gear made from the gear blank is placed in service.

My invention provides a gear blank which is less expensive than a gear blank made completely of tin bronze since only the outer rim is made of the expensive tin bronze and the innerannulus is made of the less expensive yellow brass. Additionally, gear blanks in accordance with my invention do not have the deficiencies of a composite gear blank, and there is no manufacturing cost for attaching the outer rim to the inner annulusfThus, my invention provides a unitary bimetal gear blank having an outer rim of tin bronze which is readily machinable and an inner annulus of yellow brass which has good strength. The gear blank is manufactured in an economical manner and parts are joined by a metallurgical bond which provides a good joint.

In the accompanying illustrative drawings, I have shown preferred embodiments of my invention in which:

FIG. 1 is a longitudinal section on the center line of a double hub gear blank in accordance with my invention; and

FIG. 2 is a longitudinal section on the center line of an inner flange rim gear blank in accordance with my invention mechanically attached to a double hub spider.

Referring to FIG. 1 of the accompanying drawings, my invention comprises a centrifugally cast gear blank having an outer rim 1 of tin bronze and an inner annulus of yellow brass. The inner annulus of the FIG. 1 gear blank has an angular portion 2 forming a part of web 3 and a straight portion 4 which also forms a part of the web. The straight portion 4 of the web is adjacent to hub 5, and the web and hub form the inner annulus of the doublehub gear blank. The hub has a central bore 6 to accommodate the shaft upon which the gear is mounted in final assembly. At the juncture between outer rim 1 and the angular portion 2 of the web is a diffusion zone generally designated 7 wherein the tin bronze of the rim and the yellow brass of the web are diffused to form a metallurgically bonded interface between the two metals. It is believed that the metallurgical bond results from the solidification of the dissimilar alloys, tin bronze and yellow brass. The extent of the diffusion bond is determined by process variables characteristic of centrifugal casting and is metallographically observable due to the partial diffusion of the delta phase of the tin bronze into the yellow brass.

In FIG. 2 of the drawings I have shown a modification of my invention wherein an inner flange rim gear blank 10 has a tin bronze outer rim 11 and an inner annulus 12 having an angular portion 13 and a flange 14. The inner annulus is made of yellow brass, and the tin bronze of the outer rim and the yellow brass of the inner annulus are diffused in the zone generally designated 7 to form a metallurgical bond. A plurality of angularly spaced holes 15 are drilled in flange 14 so as to be in alignment with spaced holes 20 in web 21 of hub 22, and bolts 23 with nuts 24 are used to attach the bimetal gear blank to the hub. This bi-metal inner flange rim gear blank is advantageous since the inner annulus or flange is made from the less expensive yellow brass.

The yellow brass of the inner annulus of my gear blank may be either leaded yellow brass or high strength yellow brass, sometimes called manganese bronze in the art. The type of yellow brass selected will depend upon the strength requirements for the inner annulus of the gear blank.

The composition of the tin bronze forming the outer rim of a gear blank in accordance with my invention will be within the ranges set forth hereinafter.

A preferred composition range for the tin bronze for the outer rim is 10 13 percent tin, 0 1.75 percent nickel, up to 0.25 percent phosphorus, balance copper.

As stated above, the composition of the yellow brass forming the inner annulus of my novel gear blank will depend upon the strength specifications. If high strength is not essential, leaded brass is used having a composition within the following ranges.

Leaded Brass Element Weight Copper 55 74 Tin 0 3.0 Lead 0.75 3.75 Zinc 24 38 Manganese 0 0.50 Iron O l.0 Nickel 0 0.50 Aluminum 0 L50 High Strength Yellow Brass Element Weight% Copper 55 68 Tin 1.50 Lead 0 1.50 Zinc 20 38 Iron 0 4.0 Aluminum 0 7.50 Manganese 0 5.0

Nickel 0 0.50

A preferred composition of this yellow brass is 60 68 percent copper, up to 0.20 percent tin, up to 0.20 percent lead, 2.0 4.0 percent iron, 3.0 7.50 percent aluminum, 2.50 5.0 percent manganese, balance zinc.

The novel gear blank of my invention is manufactured by centrifugal casting in a rotating mold which is constructed according to the desired final configuration of the gear blank. In centrifugally casting a gear blank according to my method, the tin bronze which forms the outer rim is added to the rotating mold first, and it is essential that there be a slight delay between the addition of the molten tin bronze and the addition of the molten yellow brass which forms the inner annulus of the gear blank. The length of this delay will depend upon the size of the gear blank being cast and the rate of rotation of the mold since the cooling rate of the metal in the outer rim is mainly determined by the amount of metal in the outer rim portion and-the time required for all of the metal to flow to the outer periphery of the mold. in general, 1 have found that a minimum delay of approximately 3 5 seconds is required between the addition of the molten tin bronze and the molten yellow brass to the rotating mold. This slight delay is essential to the creation of the metallurgically bonded interface and to prevent extensive mixing of the tin bronze and the yellow brass. The delay results in a diffusion zone in which a strong metallurgical bond is obtained between the metal of the outer rim and the metal of the inner annulus of the gear blank.

A number of advantages result from centrifugally casting a gear blank according to my invention in addition to the advantage of not having to make up sand molds. One advantage is that the more dense tin bronze inherently flows to the outer periphery of the mold and remains there. So long as the proper amount of molten tin bronze is added to the rotating mold, the outer rim of the gear blank will consist solely of tin bronze except in the diffusion zone. This means that when the gear teeth are machined on the rim, all of the metal removed will be tin bronze and the metal can be remelted. Also, as a result of centrifugal casting, there are no casting defects in the final gear blank such as inherently occur in static castings. All of the voids, inclusions, slag entrapments and other imperfections are less dense than the molten metal and remain at the inner periphery of the inner annulus of the casting and are easily removed when the gear blank is machined after casting.

A bi-metal gear blank formed by centrifugal casting is economical and has good mechanical strength in both the rim and the inner annulus. Additionally, a strong metallurgical bond is formed between the metal of the rim and the metal of the inner annulus. To illustrate the properties of a gear blank manufactured in accordance with my invention, a gear blank was centrifugally cast having an outer rim of tin bronze, a diffusion zone of tin bronze and yellow brass and an inner annulus of high strength yellow brass. The composition of each alloy was as follows:

Phosphorus Mechanical tests were conducted on metal samples taken from three areas of the blank. The results of these tests are shown in Table I.

Table l Tensile Yield Strength Strength (psi) (psi) Elongation Rim 50,525 27,340 17.4% Diffusion Zone 55,500 48,400 lnner Annulus 85,000 44,375

' No elongation results It will be seen from the above test results that the strength is excellent at all three locations tested.

The advantages of bi-metal gear blanks are that they have a lower manufacturing cost and the inner annulus has a higher strength than the tin bronze rim. The rim is relatively easy to machine since it is made of tin bronze and a strong metallurgical bond is created between the metal of the rim and the metal of the inner annulus.

While I have shown and described preferred embodiments of my invention, it should be understood that changes may be made in the specific embodiments illustrated and described so long as the changes are embodied within the scope of the appended claims.

1 claim:

1. A centrifugally cast bi-metal gear blank consisting of an outer rim of tin bronze, an inner annulus of yellow brass and a diffusion zone between the tin bronze of said outer rim and the yellow brass of said inner annulus, whereby a metallurgical bond exists between the tin bronze of the outer rim and the yellow brass of the inner annulus in the diffusion zone.

2. A gear blank as set forth in claim 1 wherein said tin bronze in the outer rim consists by weight of essentially 79 percent copper, 5.5 17 percent tin, up to 2.0 percent lead, up to 5.0 percent zinc, up to 0.25 percent iron, up to 2.0 percent nickeland up to 0.25 percent phosphorus.

3. A gear blank as set forth in claim 2 wherein said tin bronze consists of 10 13 percent tin, up to 1.75 percent nickel, up to 0.25 percent phosphorus, balance copper.

4. A gear blank as set forth in claim 1 wherein said yellow brass consists by weight of essentially 55 74 percent copper, 24 38 percent zinc, 0.75 3.75 percent lead, up to 3.0 percent tin, up to 1.0 percent iron, up to 0.50 percent manganese, up to 0.50 percent nickel and up to 1.50 percent aluminum.

5. A gear blank as set forth in claim 4 wherein said yellow brass consists of about 55.0 63.0 percent copper, up to 1.0 percent tin, 0.75 1.50 percent lead, up to 0.50 percent nickel, up to 1.0 percent iron, 1.0 1.50 percent aluminum, up to 0.50 percent manganese, balance zinc.

A gear blank as set forth in claim 1 wherein said cent lead, up to 1.50 percent tin, up to 4.0 percent iron, up to 7.50 percent aluminum, up to 5.0 percent manganese and up to 0.50 percent nickel.

7. A gear blank as set forth in claim 6 wherein said yellow brass consists of about 60.0 68.0 percent copper, up to 0.20 percent tin, up to 0.20 percent lead, 2.0 4.0 percent iron, 3.0 7.50 percent aluminum and 2.50 5.0 percent manganese, balance zinc.

8. A bi-metal gear blank as set forth in claim 1 wherein said inner annulus consists of a web section adjacent to said rim and a centrally located hub section.

9. A bi-metal gear blank as set forth in claim 1 wherein said inner annulus is a flange adapted to be connected to a hub section.

Patent No. 3,847,557 Dated er 12, 1974 William H Miller ;;lnventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 16, "8.54 should read a? 88.54

Signed and sealed this 18th day of February 1975.

(SEAL) Attest C. MARSHALL DANN RUTH C. MASON Commissioner of Patents and Trademarks Attesting Officer FORM Po wso (10.69) i uscoMM-Dc 6O376-P69 U.S. GOVERNMENT PRINTING OFFICE: 869 930 

1. A CENTRIFUGALLY CAST BI-METAL GEAR BLANK CONSISTING OF AN OUTER RIM OF TIN BRONZE, AN INNER ANNULUS OF YELLOW BRASS AND A DIFFUSION ZONE BETWEEN THE TIN BRONZE OF SAID OUTER RIM AND THE YELLOW BRASS OF SAID INNER ANNULUS, WHEREBY A METALLURGICAL
 2. A gear blank as set forth in claim 1 wherein said tin bronze in the outer rim consists by weight of essentially 79 - 90 percent copper, 5.5 - 17 percent tin, up to 2.0 percent lead, up to 5.0 percent zinc, up to 0.25 percent iron, up to 2.0 percent nickel and up to 0.25 percent phosphorus.
 3. A gear blank as set forth in claim 2 wherein said tin bronze consists of 10 - 13 percent tin, up to 1.75 percent nickel, up to 0.25 percent phosphorus, balance copper.
 4. A gear blank as set forth in claim 1 wherein said yellow brass consists by weight of essentially 55 - 74 percent copper, 24 - 38 percent zinc, 0.75 - 3.75 percent lead, up to 3.0 percent tin, up to 1.0 percent iron, up to 0.50 percent manganese, up to 0.50 percent nickel and up to 1.50 percent aluminum.
 5. A gear blank as set forth in claim 4 wherein said yellow brass consists of about 55.0 - 63.0 percent copper, up to 1.0 percent tin, 0.75 - 1.50 percent lead, up to 0.50 percent nickel, up to 1.0 percent iron, 1.0 - 1.50 percent aluminum, up to 0.50 percent manganese, balance zinc.
 6. A gear blank as set forth in claim 1 wherein said yellow brass consists by weight of essentially 55 - 68 percent copper, 20 - 38 percent zinc, up to 1.50 percent lead, up to 1.50 percent tin, up to 4.0 percent iron, up to 7.50 percent aluminum, up to 5.0 percent manganese and up to 0.50 percent nickel.
 7. A gear blank as set forth in claim 6 wherein said yellow brass consists of about 60.0 - 68.0 percent copper, up to 0.20 percent tin, up to 0.20 percent lead, 2.0 - 4.0 percent iron, 3.0 - 7.50 percent aluminum and 2.50 - 5.0 percent manganese, balance zinc.
 8. A bi-metal gear blank as set forth in claim 1 wherein said inner annulus consists of a web section adjacent to said rim and a centrally located hub section.
 9. A bi-metal gear blank as set forth in claim 1 wherein said inner annulus is a flange adapted to be connected to a hub section. 